The pro-inflammatory role of air pollutants and their modifying influence on allergic inflammation may partly explain the increase in asthma prevalence, morbidity, and mortality. Agents that have major acute effects must be considered along with an understanding of the relevant personal exposures of susceptible individuals. However, it is unclear from the epidemiological research the extent to which associations between asthma outcomes and regulated EPA criteria air pollutants such as nitrogen dioxide (NO2)are independent or attributable to other monitored criteria pollutants such as particulate matter (PM) mass, or to air toxics not usually monitored such as combustion-related organic compounds. We propose to conduct an asthma panel study with daily repeated measurements of morbidity and pollutant exposures in 64 pediatric asthmatics living in areas with high air pollution levels: an area of East Los Angeles (vehicular emission source site) and Riverside (down-wind smog receptor site). Morbidity will be measured as acute asthma symptom severity, lung function, and as-needed asthma medication use. Specific Aims include examining the relationships of daily asthma morbidity to: (1) personal exposures to airborne PM measured in real-time; (2) personal exposures to 24-hr average concentrations of PM10 elemental and organic compounds (EC-OC); (3) personal exposures to 24-hr average NO2 collected concurrently with the above exposures; and (4) NO2 and PM exposures in single as compared with co-pollutant models using the metrics in aims one-three. Strengths of independent and interactive pollutant effects will be examined to test the hypothesis that personal PM exposures, including EC-OC, modifies the respiratory health effects of personal NO2 exposures, but confounds outdoor NO2, an indicator gas for traffic-related pollutants. Personal exposure models will be developed using a nested sample of personal exposures to predict PM and NO2 exposures for the two study regions. Two panels of 32 asthmatics will be followed for two months, one at each site (total 3,584 person-days). Dosimetric models will be developed using personal and exposure-adjusted PM and NO2 above to assess whether dose estimates enhance associations. Long-term goals are to improve knowledge about the independent and combined adverse effects of particulate and gaseous air pollutants by examining acute exposures and responses using ambulatory monitoring methods.